Aerobic Units

The Jet Home Aeration Plant J-353 is an aerobic wastewater treatment system designed to reduce BOD and TSS in treated wastewater. Wastewater treatment occurs in a three compartment tank (Figure 1, side view of tank, Figure 2, schematic of system).

Figure 1 - Three dimensional representation of the Jet Home Aeration Plant (illustration provided by manufacturer).

Wastewater first enters the 476 gallon pretreatment compartment where large organic and inorganic solids settle to the bottom. A sludge layer builds up on the bottom of this compartment, and some of the organic matter is broken down by anaerobic bacteria. Fluid leaves the pretreatment compartment by hydraulic displacement into the aeration chamber through a transfer port. Each end of the port is submerged below the fluid level to prevent passage of grease and floating matter.

In the 607 gallon aeration compartment, fluid from the pretreatment chamber is mixed with aerobic sludge. The aeration chamber contains a mechanical aerator mounted above the chamber in a concrete riser. The aerator consists of an electric motor coupled to a hollow shaft with an aspirator at the end. The aspirator is submerged in the mixed liquor. Rotation of the aspirator induces mixing and the pressure differential draws air from the intake on the top of the riser down the hollow shaft and through the aspirator. As air is injected into the mixed liquor, tiny air bubbles are dispersed from the aspirator. The aeration compartment contains 19 cubic feet of special plastic media which supports the growth of aerobic bacteria. Mixed liquor circulated by the aerator passes through the plastic media as it circulates in the tank and receives treatment by the bacteria on the media. This allows aerobic degradation of the organic matter to occur.

After treatment in the aeration compartment, the treated effluent is transferred by simple hydraulic displacement to the 114 gallon settling compartment. There are two baffles between the aeration compartment and the settling compartment. The first baffle is open at the bottom and the second baffle, which is submerged in the aeration compartment, is parallel to the first baffle. Mixed liquor flows between the two baffles and maintains a circulation current in the aeration compartment. Treated effluent flows to the settling compartment through the bottom opening of the first baffle. Suspended solids and biofilm pieces in the treated effluent settle to the bottom of the settling compartment. They are returned to the aeration compartment by means of the circulation current created by the mixed liquor circulating between the two baffles.

After settling, effluent leaves the treatment compartment by hydraulic displacement. The effluent flows by gravity to the leach field or may flow to the optional JET Sand Filter for further treatment. The sand filter unit is housed in a separate tank installed near the JET aerobic unit. The Jet Sand Filter J-335 is designed to provide further treatment of aerobic treatment plant effluent. The sand filter is a small modular unit which can easily be installed in a pump chamber or dosing chamber. Effluent from the aerobic unit passes through the sand filter unit which contains a ten-inch depth of sand. In addition to providing mechanical filtration, the sand supports the growth of aerobic bacterial film which further digests sewage. The filter automatically backwashes four times daily. Backwash is transferred to the pretreatment compartment pf the aerobic unit by a backwash pump. The unit may also be configured so that the finished effluent is pumped to a dosing chamber where necessary. Final sand filter effluent BOD and TSS levels of less than 10 mg/l have been observed.

The manufacturer claims that finished effluent from the JET Aerobic unit will average 20-25 mg/L of both BOD and TSS. Preliminary results also suggest that the unit may be capable of nitrogen reduction if operation of the aerator is controlled by timer. A pilot installation in Rockland, MA has been operated so that the air supply is on during the day and is shut off at times during the night. This presumably allows the media in the tank to become anoxic during the night so that denitrification can occur. When operated in this way, an approximately 50% reduction in nitrogen was seen in limited testing. DEP has not recognized any nitrogen credit for the unit to date, however.

The JET Aerobic unit has received Remedial Use approval from DEP for use where the system design flow is 450 gpd or less. Based on the unit’s ability to reduce BOD and TSS, DEP allows a 50% reduction in leach field size or a 2 ft reduction in required depth to groundwater and certain reductions in soil requirements. DEP requires, as part of the system’s Remedial Use approval, that the system be inspected and monitored quarterly for at least three years for pH, BOD, and TSS. As part of the sales agreement, the distributor will provide two free inspection visits per year during the first two years of operation of the system. Beyond this, a maintenance contract is available for about $75 per quarter plus sampling costs. The treatment unit should be pumped out when recommended by the operator during service calls. The frequency of this procedure will be dictated by the strength of the waste stream at each unit. Pumping and other service functions are accomplished from the ground level through concrete access covers located on top of each of the three compartments of the tank.

Installation of the JET unit is simple and a septic tank is not required The unit, containing the aerator, motor, and controls, comes pre-assembled in the treatment tank. Installation of the tank is similar to installing a septic tank. If the optional JET sand filter is used, the chamber containing the sand filter must also be installed, wired, and piping for the filter backflush must be installed by the installing contractor. The JET Aerobic unit costs $5600 delivered to the site plus installation and the cost of the soil absorption system. Treatment capacity of the unit is 450 gallons per day. The JET sand filter, which is optional, costs about $775 plus installation. Local distributor of the JET Aerobic system is Stephen Nelson, Clearwater Recovery, 175 Spring St., Rockland, MA 02370 (617) 878-3849.